1. Technical Field of the Invention
This invention broadly relates to a composition for controlling the flow of water in a subsurface formation. This invention further relates to and a method of controlling the flow of water from and into a hydrocarbon containing subsurface formation. The invention more specifically relates to the use of a modified cross linked acrylic acid polymer in a method of controlling the flow of water in a high temperature hydrocarbon containing subsurface formation.
2. Description of the Prior Art and Problems Solved
It is well known in the art, that a subsurface formation which contains hydrocarbons, such as petroleum and gas, also contains salt water, referred to as formation water. It is equally known in the art, that recovery of the petroleum and gas from the formation inherently involves recovery of formation water along with the hydrocarbons. The recovery of water together with the hydrocarbons is generally regarded in the art as an undesirable aspect of the oil production process because the water, along with the desirable fluids, must be pumped from the formation to the surface where it must be separated from the desirable fluids and then it must be disposed of in some appropriate fashion. This handling of formation water is an economic and a technical burden imposed on producers which burdens, at some point in time, can become so great that oil and gas production is either terminated to avoid the water problem or steps are taken to prevent the recovery of water, or at least to reduce the volume of water recovered. Such steps have been referred to in the art as water control and/or as water shut-off.
It is also known in the art to inject water into a subsurface formation to displace oil and gas from one part of the formation to another as a step in a process of enhancing the recovery of the desirable fluid from the formation. During water injection, the injected water can at times more readily flow into and through one part of the formation as compared to another part of the formation. The formation, or part thereof, into which the water more readily flows is sometimes referred to as a thief zone. The flow, thus, is not uniform with the result that desired displacement of oil and gas is not achieved. It is believed that variations in the physical properties of the formation, for example, formation permeability and porosity, cause the mentioned non-uniform flow. Steps have been taken in the art to render the physical properties of a formation more uniform so as to cause injected water to uniformly flow into and through the entire formation. Such steps have been referred to in the art as profile modification and/or as conformance control.
The art has employed methods of water control and profile modification which methods feature the introduction of a polymeric material into a target formation to adjust the permeability of the formation. The intended result of the permeability adjustment is to block and/or to reduce the flow of water from a particular part of the formation or to make more uniform the flow of water through the formation. For purposes of this disclosure, the permeability adjustment of the formation is sometimes referred to as water flow regulation, or more simply, as water regulation.
Water control and profile modification of subsurface formations have been routinely performed using a variety of polymers, such as polyacrylamide, cellulose and xanthan gum. These polymers perform satisfactorily in shallow wells which ordinarily have low temperatures, however, they become unstable and do not perform satisfactorily in deeper wells in which temperatures are ordinarily higher. In response to the temperature problem, water control and profile modification in formations having elevated temperatures has been performed with nitrogen containing polymers developed to be stable at temperatures of about 400° F. Such polymers feature monomers, such as, 2-acrylamido-2-methyl-1-propanesulfonic acid, 4-acryloylmorpholine, 1-vinyl-2-pyrrolidone, N,N-methylene bis(meth)acrylamide, the sodium salt of vinylsulfonic acid and the sodium salt of styrene sulfonic acid.
It is known that acrylic acid polymers cannot be satisfactorily cross linked, but acrylic acid has been combined with the nitrogen containing monomers to produce copolymers having charged carboxyl sites to facilitate cross linking reactions between the copolymers. In one instance it has been reported that a blend of a nitrogen containing polymer, N,N-methylene bis(meth)acrylamide, and derivatives of acrylic acid, that is, a mixture of sodium acrylate and magnesium acrylate, has been polymerized to obtain a thermally aqueous stable gel.
It is believed that acrylic acid polymers have an excessive number of charged carboxyl cross linking sites which preferentially promote intra molecular bonding rather than inter molecular cross linking. Furthermore, acrylic acid polymers and cross linked acrylic acid polymers do not function as water control and profile modification materials, because they do not satisfactorily adhere to the walls of subsurface formations. It is believed that the inability of acrylic acid polymers and cross links thereof to satisfactorily adhere to subsurface formations is caused by the mentioned charges associated with the excessive number of carboxyl cross linking sites.
Accordingly, a problem existing in the art is the absence of a satisfactory ability to employ a stable water gel comprised of a cross linked acrylic acid polymer to regulate the flow of water into, in and through a subsurface formation, and in particular one having a temperature in excess of 400° F.